This invention relates in general to an elongated mixer block which can be used in generally horizontal rotating drums to mix, dry, heat, cool or calcine solid materials. More specifically, this invention is directed to a mixer block made preferably from a refractory material and to an improved refractory lining incorporating a plurality of the mixer blocks in a generally horizontal rotary kiln whereby more efficient and uniform calcination of fluxstone is achieved while the production of fines and dust is reduced to a minimum.
Solid particles, such as gravel, sand, stone, cementitious particles, limestone, dolomite, dolomitic limestone, magnesite, fertilizers, catalysts, and the like are frequently mixed, heated, cooled, dried or calcined in a generally horizontal rotating drum or kiln. As the drum slowly rotates, the bed of particles in the drum is carried upwardly by friction a distance along the interior periphery of the drum wall. When the weight of the bed of particles overcomes friction, the particles slide downwardly to the bottom of the drum. This process is repeated as the drum continues to rotate. There is little or no mixing of the particles. As a result, the particles on the surface of the bed can be overexposed to the environment in the drum while the particles in the interior of the bed may never be exposed to the environment in the drum. Because of the poor mixing of the particles, the bed becomes non-homogenous with respect to the particle size, environment, and temperature. A so-called kidney of non-uniform particle sizes forms, which remains in the interior of the bed resulting in non-uniform processing of the bed. The process is as a consequence inefficient and produces a non-uniform unsatisfactory product.
Means to produce a more uniform product and to improve the efficiency of operation have been devised including the use of lifters or flights attached to the interior wall of rotating drums. The lifters are designed to lift the particles in the bed a distance along the interior of the drum wall and to drop the particles to the bottom of the drum. As the particles fall, they are mixed and exposed to the internal environment of the drum. Although some improvement in uniformity of the final product is thus realized, the repeated lifting and subsequent falling result in breakage of the particles. The particles are reduced in size and a large volume of fines and dust is produced. The fines and dust particles coat the larger particles thereby interfering with the mixing, drying and calcination processes. Then, too, the dust particles are so fine that many are exhausted to the atmosphere with the exhaust gases, thereby creating a hazard to the environment. It is necessary to use apparatus to collect the dust to prevent it from being passed to the atmosphere. Operational costs are thereby increased. The dust is often a waste product and cannot be used. Fine particles often must be separated from the large particles of the material in the kiln.